A solid electrolyte capacitor which utilizes a semiconductive metal oxide such as manganese dioxide as solid electrolyte can be improved particularly in its dielectric loss and frequency-capacitance characteristics by the use of an oxide of Ru, Rh, Pd, Re, Os and/or Ir as a material of a cathode collector layer covering the solid electrolyte layer either in place of or together with colloidal carbon which is used commonly. It is preferable that a conductive layer formed on the cathode collector layer is a plasma-sprayed coating of a metal such as copper.